Electromagnetic contactor having improved knife-edge pivoted armature structure, insulating stop means and releasable arc shield



July 30, 1968 J. F. BRICK ELECTROMAGNETIC CONTACTOR HAVING IMPROVED KNIFE-EDGE PIVOTED ARMATURE STRUCTURE, INSULATING STOP MEANS AND RELEASABLE ARC SHIELD Filed June 16, 1965 2 Sheets-Sheet 1 4a ..Z- \yj3- 46 g 53! 70; 63 69 i 513 7] 74 j] 36 10 MN 4 f j 44 14 1;

Z; 4/ TT za A 42 /j I}, j 24 INVENTOR.

Jay/v E BRICK BY flndras Siarlte Afforneys July 30, 1968 F, BR. 3,395,259

ELECTROMAGNETIC CONTACTOR HAVING lMPROVED KNIFE-EDGE PIVOTED ARMATURE STRUCTURE, INSULATING STOP MEANS AND RELEASABLE ARC SHIELD Filed June 16, 1965 2 Sheets-Sheet 2 jndrus r Starks Afforws United States Patent 3,395,259 ELECTROMAGNETIC CONTACTOR HAVING IM- PROVED KNIFE-EDGE PIVOTED ARMA'I'URE STRUCTURE, INSULATING STOP MEANS AND RELEASABLE ARC SHIELD John F. Brick, Cleveland, Ohio, assignor, by mesne assignments, to A. O. Smith Corporation, Milwaukee, Wis., a corporation of New York Filed June 16, 1965, Ser. No. 464,413 7 Claims. (Cl. 200147) ABSTRACT OF THE DISCLOSURE An electromagnetic contactor including an L-shaped base to which a coil unit is secured. A spring-loaded armature pivotally secured on an adjacent ledge on the base with a movable contact held in an insulating housing on the outer end of the armature. An insulating terminal and stop is secured to the base overlying the armature plate to limit the opening of the armature. The armature is provided with a'chamfered pivot edge pivotally bearing on the offset portion of the base and with the pivot edge at an angle greater than the maximum angular movement of the armature. The fixed contact and blowout ears are secured with the blowout ears on the outer walls. An arc shield is releasably mounted to the fixed contact assembly with a pair of parallel walls extending between the outer ends of the ears to the opposite side of the aligned fixed and movable contacts.

This invention relates to a switching apparatus and particularly to an electromagnetically operated switching apparatus for use in electric power circuits requiring repeated circuit openings and closings such as starting and stopping of motors and the like.

In power circuits employing relatively heavy currents, breaking and making the circuit required rugged and reliable contactors which may operate many times over a long period without undue wear on the component parts. A highly satisfactory switching device for motor circuits and other similar power circuits is shown in the copending ap lication of Bundy et al. entitled Switching Device which was filed on Oct. 7, 1963 with Ser. No. 314,212 and which is assignedto a common assignee with the present application. The switching device disclosed therein employs a generally modular construction for the several operating members such as the mov able and fixed contacts with attachment means providing electrical insulation for the supporting base or mounting member. In addition, as required in the opening of high current circuits, an improved arc blowout system and an are running and shielding system is provided for rapid dissipation of any are which may form as the contacts open under load currents.

The present invention is particularly directed to an improved contactor and particularly to an improved mounting of the movable contact unit and of the arc dissipating apparatus.

Generally, in accordance with the present invention, a suitable mounting base formed of a magnetic material is provided with a core member on which an operating coil is wound. An armature is pivotally secured overlying the coil upon the adjacent edge of the mounting plate and a contact support assembly or arm which projects parallel from the outer surface of the end of the mounting plate. The movable contact is resiliently disposed within an insulating housing which in turn is secured to the outer or forward end of the armature plate. A member formed of an insulating material is secured to the outer ends of the extension overlying an intermediate 3,395,259 Patented July 30, 1968 portion of the armature plate and projects downwardly to define a stop which determines the maximum opening or outward pivotal movement of the armature plate. A resilient member acts between the plate and the insulating body to continuously urge the plate to a normally open contact position.

In accordance with an important aspect of the present invention, the pivot edge of the plate is provided with a chamfered edge defining a knife edge on the under surface of the plate pivotally bearing on the offset portion of the mounting plate. The chamfered edge is selected to have an angle greater than the maximum angular movement of the armature plate. Consequently, when the armature moves to the open position an air gap is maintained between the armature plate and the adjacent offset portion of the mounting plate. This is of substantial significance in that it essentially prevents formation of a magnetic flux path tending to magnetically lock the armature in the open position and interfering with optimum operation of the contactor. In accordance with the present invention and as generally disclosed in the above identified application, the fixed contact is secured to the mounting plate by a separate insulating support mounted to the base portion of the mounting plate. In accordance with the present invention, the fixed contact support includes a plurality of parallel outwardly projecting side walls with a blowout coil mounted therebetween by a suitable insulated nut and bolt assembly or the like. The blowout assembly of the present invention includes the blowout ears secured to the outer walls by the same nut and bolt assembly to maintain a continuous magnetic flux path. A generally U-shaped arc runner is mounted to the fixed contact base overlying the blowout coil. The fixed contact is secured to the runner in alignment with the outer end of the movable contact arm. An arc shield consisting of a pair of parallel walls is releasably mounted to the fixed contact assembly with the walls extending between the outer ends of the ears and thus enclosing or disposing the walls to the opposite side of the aligned fixed and movable contact portions. The shield has the side walls extending generally around coextensive with the outer portion of the runner and is clamped therebetween by a leaf spring or the like secured to the fixed contact mounting member and extending in generally paralleled relation with the adjacent portion of the arc runner to define a resilient clamping surface therebetween. Additionally, the outer portion of the shielding walls is joined by a lateral wall about which a forward or movable contact are runner is secured with the runner projecting inwardly adjacent the outer end of the contact arm. This provides an integral one-piece arc chute construction having the movable contact are runner formed as an integrated part of the element without the necessity for the separate bolted type connection generally heretofore employed in connection with contactors of the prior art.

The present invention is thus directed to a simplified andumproved power circuit contactor for opening and closing of power circuits and which is constructed of a modular construction to permit ready maintenance repair and the like. The several components of the apparatus are readily constructed and assembled in accordance wlth requirements for mass production and as a result of the reduction in the number of components from that heretofore employed in similar contactors and simplification of parts reduces the overall cost of the initial constructions.

The drawing furnished herewith illustrates a preferred construction of the present invention incorporating the above advantages and features of the present invention as well as others which will be clear to those skilled in the art from the following description thereof.

In the drawing:

FIG. 1 is a side elevational view of a switching device constructed in accordance with the present invention;

FIG. 2 is a bottom view of the apparatus shown in FIG. 1;

FIG. 3 is an enlarged vertical section taken on line 33 of FIG. 2;

FIG. 4 is an enlarged fragmentary view clearly illustrating the pivotal mounting of the armature plate of the present invention; and

'FIG. 5 is a fragmentary sectional view taken generally on line 5-5 of FIG. 3 showing details of construction.

Referring to the drawings and particularly to FIGS. 1 and 2, the present invention is shown as an electromagnetic contactor which will normally employ direct current (D.C.) operating power for opening and closing of the circuit in response to an electrical signal. The illustrated contactor has been particularly designed and satisfactorily employed in the operation of motor circuits for substantial periods of time and with an exceedingly large number of opening and closing operations without the necessity of attendance and repair.

The illustrated contactor generally includes an L-shaped mounting frame or plate 1 formed of a suitable magnetic material. An electromagnetic coil unit or assembly 2 is secured to the plate adjacent the junction of the two legs of the plate and projects parallel to the offset leg. An armature assembly 3 is pivotally secured to the outer end of the lateral arm of the plate and extends over the coil unit 2 for selective pivotal movement with respect to the coil assembly. Assembly 3 is resiliently biased in spaced relation to the coil unit 2 and is attracted thereto in response to the field established by energization of the coil unit. A movable contact 4 is secured to the outer or free end of the assembly 3 in operative relation with a fixed contact 5. A blowout assembly 6 is formed as an integrated part of the mounting for the fixed contact 5 to rapidly dissipate any arc which might be generated between the movable contact 4 and the fixed contact 5 as more fully developed hereinafter. An arc shield 7 is also releasably secured as a part of the mounting of the fixed contact 5 and completely encloses the interengaging contact members to enclose such arcs.

Generally, in accordance with the operation, the mounting plate 1 is secured to a suitable mounting surface and the electromagnetic coil unit 2 is connected in a control circuit, not shown. The armature assembly 3 is normally spaced from the electromagnetic coil assembly 2 to space contacts 4 and 5 and maintain an open circiut condition. When the coil unit 2 is energized, it attracts the armature assembly 3 and closes the contacts to complete the motor circuit or the other circuit in which the main contacts are connected. When the coil unit 2 is de-energized, the circuit will rapidly open as a result of the resilient mounting of the assembly 3 to open the circuit. The are shield 7 encloses any are formed between contacts 4 and 5 and the blowout assembly 6 will rapidly dissipate the are.

More particularly and as more clearly shown in FIG. 2, the L-shaped mounting plate 1 is provided with apertured mounting tabs 8 through which the base portion of the mounting plate 1 is secured to a suitable vertical mounting surface. The plate 1 is mounted with the shorter or lateral horizontal leg 9 projecting outwardly along the bottom of the assembly. A central pole or core 10 of unit 2 is shown bolted to the one leg of the mounting plate 1 and extends outwardly parallel to and coextensively with the opposite or horizontal leg 9'. A direct current coil 11 is telescoped or wound over the core 10 and secured thereon by a small clamping disc 12 which is bolted or otherwise secured to the outer end of the core with a small nonmagnetic spacer 13 disposed between the clamp 12 and the adjacent end of the core. A round leaf spring member 14 is preferably disposed between the base of the mounting plate 1 and the adjacent coil 11. The coil is provided with the usual input terminals for connection of the coil into the circuit for generation of a magnetic flux through core 10, plate 1 and armature assembly 3, to be presently described, for attracting assembly 3 and moving contact 4 into engagement with contact 5.

More particularly, the armature assembly 3 includes an armature plate 15 having a width generally corresponding to the width of the mounting plate 1 and pivotally mounted to the outer end of the lateral frame leg 9 with respect to the core 10. The outer end of the frame leg 9 defines a flat pivot ledge 16 adjacent a bifurcated outwardly projecting support plate 17 which is secured as by bolts 18 to the leg 9 and constitutes an offset extension of the frame leg 9. The illustrated plate member 17 includes a base portion aligned with the outer end of the leg 9 and a pair of L-shaped legs 19 which project outwardly therefrom and then inwardly in spaced parallel relation to the armature plate 15 to define inwardly extending portions disposed toward the core. A stop and connector support 20 is secured between the outer end of the inwardly bent ends of the L-shaped legs 19 and projects inwardly towards the plate to form a stop defining the maximum outward pivotal or angular movement of the armature plate 15 with respect to core 10.

In accordance with an important aspect of the illustrated embodiment of the invention, the pivot edge of the plate 15 in alignment with legs 19 is chamfered as at 21 with an angle in excess of the angular movement of the maximum angular'movement of the armature plate with respect to the core 10. The chamfered edges 21 form a pair of pivotal knife edges pivotally supported engaging the junction of the outer end of leg 9 and the projecting legs 19 which form an offset portion in the total assembly, as shown in FIGS. 3 and 4. The plate 15 is held in the assembled relation by a pair of laterally bent legs or tabs 22 which project laterally adjacent the outer portion of the plate 17. An oppoistely bent and angularly related tab 23 between the tabs 22 is also provided with a coil spring 24 compressed between the tab 23 and an adjacent portion of the support 20.

In accordance with the present invention, the support 20 is formed of a high strength insulating material and preferably is formed of a chopped glass filled polyester resin which is hot molded to increase the strength of the assembly. Generally, the support 20 includes a central body portion extending in opposite directions between the inwardly bent portions of legs 19 and having oppositely extending central flanges 25 secured to the overlying portions of legs 19 by suitable attachment bolts 26 which pass through the flanges and thread into the suitably tapped openings in the legs 19. The flanges 25 preferably include forward walls 27 which extend parallel to the bolts to define a locating edge abutting the inner end of the corresponding leg 19. A cylindrical recess 28 is formed in the back side of support 20 to accommodate the outer end of the spring 24.

In operation, the coil spring 24 continuously urges the 1 armature assembly 2 to pivot outwardly from the core 10; clockwise as viewed in FIG. 3. The chamfered pivot edge 21 of the plate maintains an air gap 29 between the plate and the adjacent portion of the path defined by the projecting leg 19 and thereby prevents magnetic locking of the armature assembly in the open position. When it is desired to close the contacts 4 and 5, the coil 11 is energized, attracts the armature plate 15 and moves the movable contact 4 into engagement with the fixed contact 5.

In the illustrated embodiment of the invention, the movable contact 4 is resiliently mounted in a generally rectangular collar or housing 30 having laterally projecting mounting flanges 31 which are secured to the armature plate by suitable bolts 32 which pass through the flanges 31 and thread into appropriately tapped openings in the outer portion of the armature plate 15. The housing 30 is mounted immediately forwardly of the support 20 and opening toward the fixed contact 5. The collar 30 includes a forward depending wall 33 extending downwardly over the adjacent portion of the armature plate and an inner pivot recess 34 at the opposite end of the bottom wall. Contact 4 is a metallic bar-like member having an integral depending knife edge 35 disposed in the recess 34 and extending outwardly in overlying relationship to the fixed contact 5. A spherically :faced button 36 is integrally secured to the outer end of the arm in alignment with the fixed contact 5. A levelling projection 37 is integrally formed to the underside of the arm in spaced relation to edge 35. A braided strap 38 of aluminum, copper or the like is provided with end lugs 39. One end of strap 38 is secured to the contact 4 between the edge 35 and the levelling projection 36 by a suitable bolt 40 which passes through the strap and threads into the contact arm. The opposite end is secured to an outer wall 41 of support 20 by a nut and bolt assembly 42. A coil spring 43 acts between the back side of the contact 4 and the outer wall of the support 20 to continuously and resiliently hold it therein for limited pivotal movement about the pivot edge 35. A wear and locating bracket 44 is disposed between the coil spring 43 and the wall of the support 20 with an inwardly projecting locating flange. The head of the bolt 40 serves as a locating and retaining member for the opposite end of the coil spring.

The opposite end of the strap lead 38 is connected by the nut and bolt unit 42 to the top wall of the outer wall of the support 20 in common with a lead connecting conductive strip 45 which projects laterally to opposite sides of support 20 for connection of the movable contact 4 in one side of the circuit which is completed through contact 5.

In the illustrated embodiment of the invention, the fixed contact 5 is an L-shaped conducting strap attached to the inner leg of a U-shaped fixed contact arc runner 46 and mounted to plate 1 in common with the blowout unit 6 and the arc shield 7 by a separate insulating support 47. Contact 5 includes a spherical faced contact button 48 aligned with the contact button 36 of the contact 4.

Generally, the support 47 includes a base portion bolted or otherwise secured to the mounting plate adjacent the coil 11. The support 47 is generally formed of a suitable insulating material such as the previously described glass reinforced polyester resin to provide a high strength insulating member. The support 47 includes parallel side walls 49 extending from the base portion in the direction of the movable contact 4 but terminating in spaced relation thereto. A blowout coil 50 is wound on an insulating support and secured in place between the side walls 49 by a nut and bolt unit 51. The support includes an inner magnetic core 52 through which the bolt of unit 51 passes and an outer insulating sleeve 53 on which the coil is wound. The side walls 49 are notched as at 54 to accommodate the sleeve 53. The core 52 is slightly longer than sleeve 53 and projects outwardly into firm abutment with suitable magnetic blowout cars 55, as most clearly shown in FIG. 5.

The coil 50 is generally a strip member spirally wound on its edge on the sleeve 53. One end of the coil 50 extends circumferentially into the base of the support 47 and is secured to a nut and bolt connector unit 56 which extends completely through the base. The opposite end of coil 50 extends toward the coil 11 between the side walls 49 and is bent inwardly, as shown in FIG. 5, adjacent the rear arc runner 46 and is bolted or otherwise secured thereto and thereby to the fixed contact 5.

Blowout ears 55 are secured to the outer surface of the side walls 49 by the nut and bolt unit 52. The exterior surface of walls 49 is provided with guide projections 57 spaced in accordance with the width of the ears 55. One of projections 57 terminates inwardly of the end of the ear 55 which includes a lateral lip 58 extending beneath the projection to lock the assembly to the walls 49, as shown in FIG. 1. The ears 55 project outwardly from the walls 49 on the opposite sides of the contact buttons 36 and 48 and create a magnetic flux or field functioning to control the lateral path of any are created between the contact buttons and further in cooperation with the arc runner 46 and shield 7 rapidly elongates and extinguishes the are without burning and damaging of the contact buttons. The mounting of the blowout ears by the nut and bolt unit 52 with the projecting sleeve 53 provides a continuous fiux path while simultaneously supporting and insulating the coil from the ears. This dual functioning permitted by the illustrated embodiment of the invention simplifies the mounting and construction of the arc blowout structure.

The rear or fixed contact arc runner 46 is generally a U-shaped member mounted in spaced relationship to the coil 50 and overlying the support member. The runner 46 includes a base portion connecting side arms, the ends of which terminate in inwardly projecting mounting tabs 59 bolted or otherwise secured to the body portion of the support 47.

A generally L-shaped leaf spring 60 is secured to an outer ledge on the support 47 by the bolt connection to the one mounting tab 59 and extends generally parallel with the outer leg of the runner 46. The outer end of spring 59 terminates in a bent portion 61 defining a clamping projection extending inwardly toward the arc runner and serving to resiliently clamp the arc shield 7 overlying the movable and the fixed contact buttons 36 and 48.

The are shield 7 generally includes a pair of laterally spaced plate-like side walls 62 fitted between the ears and having recessed portions 63 defining rear leg portions extending about the outer leg of the arc runner 46. The side walls 62 are connected by an integral clamping wall 64 adjacent the arc runner 46. The clamp wall 64 includes inner ledge or projections 65 releasably disposed in holding engagement with corresponding clamping notches or ledges 66 formed on the opposite edges of the adjacent portion of the fixed contact runner 56. An outer ledge 67 on wall 64 overlies the bent end 61 of the leaf spring 59 to limit the downward or inward movement of the shield '7. The shield 7 is removed by grasping the arc shield and lifting up slightly to disengage the projections 64 from notches 66 and permit withdrawal from between the spring 59 and runner 56.

A forward or movable contact are runner 68 is mounted adjacent the opposite end of the shield 7. The are runner 68 is generally a strap slightly wider than the spacing of the walls 62 and includes a U-shaped portion folded over a lateral wall 69 with the adjacent side wall 62 grooved to accommodate the strip. The one end of the runner projects inwardly between walls 62 and terminates in a contact end 70 spaced from the outer end of the contact 4. The opposite end of the runner 68 is bent laterally outwardly from the wall 69 to form a connecting tab 72 adjacent a connecting wall 73 integrally formed with the side walls 62 in outwardly spaced relation from the wall 69. A nut and bolt unit 74 interconnects a pigtail 75 to the tab 72 of the runner 68. The opposite end of the pigtail 75 is connected in common with the braided strap lead 38 to the connector unit 42.

The innermost edge of the arc runner 68 is positioned closely adjacent the movable contact 4 as the contact moves to the open position and is positioned within the open space defined by the side walls 62 to provide an arc elongation and confining path. The shield 7 is generally formed of any suitable material such as a chopped glass filled polyester resin which produces an extinction aiding gas when subjected to the heat of an arc.

The mounting and operation of the illustrated embodiment of the invention is briefly summarized as follows. The incoming power leads, not shown, are connected to the connector unit 42 and to the rear arc runner connector to provide connection respectively to the movable contact 4 and the fixed contact 5, in series with blowout coil 50. The coils 11 of the electromagnetic assembly 2 are connected to the signal or control circuit. Referring particularly to FIG. 3, the armature assembly 3 is shown in the drawing in the normal position with the coil 11 de-energized and contacts 4 and 5 open. The contacts remain in the open position as a result of the spring bias of the coil spring 24 as well as the gravity forces. An air gap 29 is maintained between the pivotal mounted edge of the plate 15 and the return path defined by the support plate 17 and the mounting plate 9. When the coil 11 is energized, a magnetic circuit is established tending to draw the armature 15 rapidly to the core 10. The illustrated mounting provides a relatively frictionless pivotal mounting of the armature plate 15 as a result of the knife edge provided by the edge 21.

The pivotal movement of the armature assembly causes the contact buttons 36 and 38 to disengage. The armature plate 15 moves beyond the position at which the fixed contact is engaged to pivot contact 4 in a clockwise direction as viewed in FIG. 2 and compresses the contact spring 43. The compressed spring 43 securely holds the contacts closed in the presence of vibration or the like. Further, the pivotal mounting of the units provides a wiping action as the contacts 4 and 5 close, which will tend to disrupt or remove oxide coatings or other accumulations which may form on the contact buttons to provide reliable circuit completion.

When the coil is de-energized, the coil Spring 24 rapidly moves the armature plate to the normally open position engaging the insulation housing 20. Any arc which is formed between the contacts 4 and 5 is rapidly dissipated as a result of the magnetic field established by the arc blowout coil 50 and ears 55 and the confinement to the arc runners by the shield 7. The are will be transferred to the arc runners 46 and 68 to protect the contacts as such, with one end transferred from the fixed contact 5 to the rear arc runner 46 and the opposite end transferred from the movable contact 4 to the front arc runner 68. The magnetic flux created by the blowout coil 50 acts to extend and elongate the arc confined between the walls 62 of the arc shield 7 until it is completely extinguished. The are barriers formed by walls 64 and 69 which join the opposite ends of the arc shield side walls 62 limit the movement of the arc beyond the limits of the arc runners to any other operating components.

As previously noted, the present invention has been found to provide a highly reliable and long life operating contactor and in fact has been connected and operated to start and stop a motor in excess of one million actuations without maintenance requirements. The simplicity and modular construction of the system permits ready assembly, maintenance and replacement of one or more of the parts if required.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A switching device comprising:

first and second contacts, the first contact of which is immobile and the second of which is mobile,

an arc blowout assembly connected to the immobile contact and operative to produce an arc dissipating flux; the blowout assembly including an insulating sleeve having a blowout coil wound thereon and connected in circuit with the first contact and an inner magnetic core projecting outwardly of the sleeve, said blowout assembly including a base of insulating material having spaced parallel walls with the coil disposed therebetween and having blowout ears secured to the outer surface of the walls and abutting said magnetic core,

a fixed contact are runner associated with the blowout coil and ears, an electromagnetic unit having a generally L-shaped frame with a coil mounted on a first leg and lying adjacent the second leg, said frame including an offset extension of the last named leg defining a pivot ledge,

means securing the base of the blowout assembly to the first leg,

an armature plate including .a chamfered outer edge wall defining a pivot edge disposed in the corner of the pivot ledge with the chamfered edge facing the offset extension,

an insulating stop member secured to said extension and overlying the armature plate to limit the pivotal movement of the plate to an angle less than that of the chamfered edge,

a contact support secured to the outer portion of the plate,

a contact arm pivotally mounted on the support,

resilient means clamping the arm to the support, and

an arc shield associated with the blowout assembly and the contacts; the arc shield having a movable contact are runner which is adapted to receive an electric are from the movable contact upon the opening thereof and to act with the fixed contact arc runner of the blowout assembly to elongate and dissipate the are formed by the separation of the contacts.

2. The switching device of claim 1 wherein:

said fixed contact arc runner includes an outer leg member parallel to the second leg of the frame,

a clamping leaf spring mounted in spaced parallel relation to the outer leg member, and

said arc shield includes a leg portion resiliently clamped between the leaf spring and the outer leg member.

3. A switching device comprising:

first and second contacts, the first contact of which is immobile and the second of which is mobile,

an arc blowout assembly connected to the immobile contact and operative to produce an arc dissipating flux; the blowout assembly including an insulating sleeve having a blowout coil wound thereon and connected in circuit with the first contact and an inner magnetic core projecting outwardly of the sleeve, said blowout assembly including a base of insulating material having spaced parallel walls, corresponding notches in the outermost edges with the coil disposed therebetween and having blowout ears disposed adjacent the outer surface of the walls and abutting said magnetic core, a nut and bolt assembly passing through the magnetic core to clamp the ears abutting the ends of the magnetic core and to lock the coil between the walls,

a U-shaped arc runner secured to the base and overlying the blowout coil,

an electromagnetic unit having a generallyL-shaped frame with a core secured to a first leg and extending parallel to the second leg, said core terminating in alignment with the second leg and having a coil mounted thereon, an extension plat-e secured in abutting engagement with the second leg and projecting outwardly therefrom,

means securing the base of the blowout assembly to the first leg in spaced relation to the coil,

an armature plate including a chamfered outer edge Wall defining a pivot edge disposed in the corner of the end of the second leg and the extension plate with the chamfered edge facing the extension plate,

an insulating stop secured to said extension and overlying the armature plate to limit the pivotal movement of the plate to an angle less than that of the chamfered edge,

an insulating contact collar secured to the outer end portion of the armature plate,

a metal contact arm pivotally and resiliently mounted on the contact coller, and

an arc shield associated with the blowout assembly and the contacts; the arc shield having a single piece of strap constituting an arc runner which receives the end of an electric arc from the movable contact upon the opening thereof and coacts with the arc runner of the blowout assembly to elongate and dis- 9 sipate the are formed -by the separation of the contacts.

4. The switching device of claim 3, wherein:

a leaf spring member is secured to the base of the blowout assembly and extends in parallel spaced relation to an outer leg of the U-shaped arc runner,

said arc shield includes a depending leg portion and a pair of spaced side walls joined by a laterial clamping wall in the leg portion and a lateral arc runner wall in the inner top portion, the clamping wall insupport member in engagement with the ends of the magnetic core,

an arc shield releasably secured to the outer portion of the arc runner and extending between and outwardly from the blowout ears,

a movable contact secured to the mounting member in opposed relation to said fixed contact, and

a movable contact are runner secured to the arc shield in outwardly spaced relation to the movable contact.

6. The switching device of claim 5 wherein:

eluding projections on the inner surface releasably a leaf p g member is secured to the Support membfif engaging notches on the edges of the arc runner and and eXtehdS in Parallel Spaced relation to an Outer engaged by the leaf spring to resiliently mount the leg of the P arc arc shield, and said arc shield includes a depending leg portion and said movable contact are runner being secured to the a P of spaced Side Walls joined y a later 31 plateral arc runner wall and extending inwardly tohlg Wall in the leg Portion and a lateral arc funnel ward the mov bl t t, wall in the inner top portion, the clamping wall in- 5. A switching device including a magnetic arc blow- Cludhlg Projections 011 the inner Surface feleasably out assembly forming a part of a fixed contact, comengaging notches 110 the edges f the are runner and prising: engaged by the leaf spring to resiliently mount the a mounting member, are shield, and an insulating support member having a base secured to Said movable contact are Tunnel being secured to the th ti member and a i of outwardly lateral arc runner wall and extending inwardly tojecting parallel Walls having aligned openings, Ward the movable Contacta mounting unit extending through said parallel Walls The Switching device of claim 6 wherein d are runner wall of the arc shield is spaced inwardly of the outer edge and a contact wall is integrally formed in outwardly spaced relation, and

said movable contact are runner is a U-shaped strap disposed over the arc runner wall and includes a lip abutting the underside of the contact wall.

in spaced relation to the base and having an insulating outer sleeve and an inner magnetic core projecting laterally of the sleeve and through aligned openings in said parallel walls, the length of the magnetic core corresponding to the distance between the exterior surfaces of said parallel walls,

a U-shaped arc runner overlying said member and having a base portion connected to a pair of side arms having ends secured to the base,

a fixed contact secured to the arc runner and having a References Cited UNITED STATES PATENTS 1,640,556 8/1927 Rile et a1. M 200-147 X portion located ad acent the base portion of the 1869552 8/1932 Enisy 200 147 X m t N d t 2,020,935 11/1935 E1115 et al. 200 144 a magnet 9 Supp" e Sal SPPPM 2,374,017 4/1945 Iglehart et al. 2 200 147 X member within the arc runner and between said par- 2 523 9/1950 200 147 llel walls and having one end connected to said arc lerc-e n a 3,284,601 11/1966 Harrington 200144 runner 3,325,616 6/1967 Bundy et al. 200-147 a pair of blowout ears disposed adjacent the outer surface of said parallel walls and projecting outwardly BER S.MA ,P Ea in parallel relation, said ears being mounted on said R0 T CON nmary x mmer 

